查获的资料
By placing the PERIOD constraint on the input clock, the Xilinx tools automatically:
• Derive a new PERIOD constraint for each of the DLL/DCM/PLL output clocks
• Determine the clock relationships between the output clock domains, and
automatically perform an analysis for any paths between these clock domains.
嘻嘻,
1,offset out 的参考时序是pad端输入时钟这个明白否?
2,比如说,约束的值是10ns,这个10ns是相对于clk_in(pad),如果clk_in经DCM延时了4ns,变成了clk_dcm,输出的数据是以clk_dcm时钟的沿打出的,那么布局布线时数据输出延时就是6ns,软件自动算上了DCM的延时4ns。明白了吧!